THE ETE.] 



THE HOESE, AND 



[the ETE. 



over the eye, showing that it has no separate 

 movement, but is dependent on the retractor 

 muscle, and performs its functions by moving 

 a part to which it is least attached. 



The lachrymal glands ax'e placed above the 

 levator palpelrce, lying close to the sclerotic 

 coat, and moisten the eye. 



The eyelids are peculiar in the horse. The 

 bottom one has no lashes, but the upper one 

 has a double row iu the centre, but not extend- 

 ing from cantJius to cantJius. They are seldom 

 diseased, or even the cause of disease. 



The conjunctiva is immediately connected 

 with the eyelids, the haw, and the orbit. It 

 possesses three different structures ; that is, 

 three separate degrees of vascularity. It lines 

 the inner surface of the eyelids, and covers the 

 eye-ball, being reflected over every part. This 

 membrane is highly vascular in that part 

 ■which lines the eyelids, and is less so over the 

 opaque cornia, and still less over the transpa- 

 rent cornia, never admitting red particles of 

 blood, unless in a state of inflammation. The 

 eyelids possess a secretion of their own, to 

 protect them from the tears, which, though 

 congenial to the eye, are not so to the edges 

 of the palpehrcB. It is a well-known and 

 somewhat singular fact, indicating the dif- 

 ferent degrees of susceptibility to which 

 different parts of the animal structure are 

 liable — that the salt that is in tears will at any 

 time inflame the cheek, but not the eye ; whilst 

 warm water applied to the eye, will inflame 

 it, f^nd be congenial to, and relieve the cheeks. 

 The apparent use of the eyelid is to pro- 

 tect the eye from foreign matter, and also to 

 regulate the admission of light. Independent 

 of these, the inner surface of the upper eye- 

 lids, covered by the conjunctiva, is connected 

 with the tears, which flow between the eye- 

 ball and the lid, the conjunctiva being thus 

 prevented from coming in contact by a fluid. 

 The eyelids also secrete a fluid of their own, 

 which prevents any tendency to irritation. 

 The action of the lachrymal glands is carried 

 on, at intervals, even in sleep, though there 

 may be but little wanted; but any foreign 

 matter, even the wind, will excite their action. 

 This is occasioned by the nerves of the eye- 

 ball being irritated, and the tears, iu conse- 

 quence, being thrown out to alleviate such 

 irritation. Between these glands aud the 

 200 



mental character of the horse, there is also 

 great sympathy; and when their action is 

 excited, so that the secretion has become too 

 great to be carried off by the nose, the tears 

 flow over the cheeks, which constitutes weeping. 

 This secretion is also aflected by the action of 

 the retractor muscle, which, operating with 

 the adductor muscle, the eye-ball is brought 

 to the inner canthus, and the haw forced over 

 the eye-ball. Extraneous matter very seldom 

 occasions blindness ; for the tears and the eye- 

 ball moving in one direction, and the haw in 

 a contrary one, any such matter is quickly 

 dislodged. 



The use of tears is to keep the parts moist 

 and transparent, and to remove the waste from 

 evaporation, which is always going forward in 

 moist external surfaces. Having performed 

 their office of lubricating the eye-ball, and the 

 parts attached, they pass into the duct, called 

 puncta lachrymalis, situated at the inner 

 canthus of the eye. This duct in the horse is 

 little larger than in the human subject, and 

 passing through a canal, partly bony and 

 partly membranous, terminates at the lower 

 end of the nostrils, much increased in size. 

 The construction of this junction in man is 

 much more complicated than it is in the horse, 

 and is very frequently subject to disease by 

 becoming obstructed. In the horse this very 

 seldom occurs ; and when it does, it is attended 

 with but very trifling inconvenience. The 

 action of the haw takes place from any cause 

 which produces pain or inflammation ; and this 

 may be continued so long, that the retractor 

 and adductor muscles will permanently con- 

 tract, when the haw, being completely power- 

 less of itself, is left protruded out. When 

 this is the case, there is no difficulty or danger 

 in cutting it out with a pair of scissors. 



In the horse there is no opaque cornea 

 visible; whilst in man, it constitutes a promi- 

 nent feature of the organ ; aud although it does 

 not appear to give any additional perfection to 

 the vision, it adds greatly to the beauty aud 

 expression of the eye. 



The transparent cornea is more or less con- 

 vex iu all animals. In horses, it is not cir- 

 cular, but horizontally oblong, being more 

 contracted at the outer than the inner part. 

 The ball of the eye is also denser aud more 

 trausparent. By a law of optics, the rays of 



